Leave Signed Response unchecked.
When the Signed Response checkbox is unchecked, only the assertion is signed. When the Signed Response checkbox is checked, the entire response is signed.

The default Name ID is the primary email. Multi-value input is not supported. You can change the Name ID mapping as per your requirement. Custom attributes of the user schema can also be used after creating them via Google Admin SDK APIs. The custom attributes for the user schema need to be created prior to setting up the Lucidchart SAML application.